1. Gene linkage and polyploidy
Ch 10.3

2. Gene linkage Chromosomes contain genes for a lot of proteins
Genes that are on the same chromosome are usually inherited together.
These genes are considered linked.

3. Polyploidy
Occurrence of one or more extra sets of all chromosomes in an organism
Triploid= 3n. 3 complete sets of chromosomes
Earthworms, goldfish,
some flowering plants

4. Complex Patterns of Inheritance
Chapter 11.2

5. Extending Mendelian genetics
Mendel worked with a simple system
traits were controlled by a single gene
each gene had only 2 alleles, one of which is completely dominant to the other
The relationship between genotype & phenotype is rarely that simple

6. Incomplete Dominance
Dominant and recessive phenotypes are blended in heterozygotes
Example: In snapdragons, the alleles for red flowers (CR) and white flowers (CW) both influence the phenotype
CRCR = red
CWCW = white
CRCW = pink

7. Incomplete dominance P F1 100% F2 1:2:1 X true-breeding white flowers
Incomplete dominance
true-breeding
white flowers
true-breeding
red flowers X P
100% pink flowers F1
generation
(hybrids)
100%
self-pollinate
25%
red
50%
pink
25%
white F2
generation
1:2:1

8. Codominance
Occurs when both alleles for a gene are expressed at the same time in heterozygotes
Roan horses are a combination of white and red horses
Instead of blending they have patches or red or white hair.

9. Codominance – Sickle cell anemia
Blood is sickle shaped
Decreased ability to transport oxygen
block circulation in small blood vessels

10. Codominance – Sickle cell anemia
Homozygous dominant (SS)– healthy
Heterozygous (Ss)– some sickled some healthy blood cells.
Malaria resistant.
Homozygous recessive (ss)– all sickled cells. Fatal.

11. Multiple Alleles
Some traits are determined by more than two possible alleles.
Example: human blood type (ABO)
Alleles:
IA, IB, i
Rh +/- gene
genotype
phenotype
Donor status
IA IA , IA i
type A A
IB IB, IB i
type B B
IA IB
type AB
universal recipient
i i
type O
universal donor

12. Multiple Alleles – rabbit coat color
Four possible alleles for coat color:
C, cch, ch, and c
Dominance order : C > cch > ch > c
Increases number of possible genotypes and phenotypes

13. Epistasis One gene masks another coat color in laboradors - 2 genes
Gene 1 – pigment (C) or no pigment (c)
Gene 2 – more pigment (black=B) or less (brown=b)
If gene 1 is recessive (cc) the dog will be yellow lab no matter what gene two is.
If gene 1 is dominant (Cc or CC) could be black or chocolate lab depending on gene 2

14. Epistasis in Labrador retrievers
Epistasis in Labrador retrievers

15. Chromosomes in Humans Humans have 23 pairs of chromosomes
22 pairs of autosomes
1 pair of sex chromosomes
Contain genes that determine gender
XX = female, XY = male

16. Sex determination 50% chance for male 50% chance for female
Which parent determines gender?

17. Examples: color-blindness, hemophilia
Sex linked traits
Sex-linked traits are coded for by an allele on a sex chromosome.
Examples: color-blindness, hemophilia
X linked traits more prevalent in males than females.

18. Polygenic inheritance
Some phenotypes determined by additive effects of 2 or more genes for a single character
human traits:
Skin color
Height
Eye color
Intelligence

19. Chromosomes and Human Heredity
Chapter 11.3

20. Mutations Sex-cell mutations: occur in gametes Affect offspring only
Somatic-cell mutations: occur in body cells Affect the organism only, not inherited
Lethal mutations cause death
Some mutations are beneficial give organism an evolutionary advantage

21. Chromosome Mutations Deletion – loss of a piece due to breakage
Inversion – a piece breaks off, flips, and reattaches
Translocation – a piece breaks off and reattaches to a
non-homologous
chromosome

22. Chromosome Mutations
Nondisjunction – a chromosome fails to separate from its homologue during meiosis
One gamete gets an extra copy, the other gets no copies

23. Nondisjunction – Down’s Syndrome
Trisomy 21

24. Fetal testing
Testing can be done on fetus before it is born to examine chromosomes.
Testing can highlight genetic disorders
Testing can be dangerous to mother and fetus.

25. Karyotype Studies A method to study the whole chromosome
Pairs of homologous chromosomes are lined up in decreasing size to produce a micrograph
Used for fetal
Testing

26. Karyotype Studies

27. Telomeres
Telomeres are the protein and DNA caps on the end of chromosomes.
Involved in aging of cells.